UNLESS the "Item Description" has changed, or you accidentally placed too high a bid in error (pressed wrong key) I believe you can't. If you wait longer than a couple hours after your bid is placed in error, you're still stuck. Maybe you can try to prove to eBay that your bidder ID was hacked.. Don't know.
A common way to uncover a high reserve without being stuck for the price, is "accidentally" enter an extra zero or two on your bid, see reserve, then retract the bid... I thank Ken Denny for that tip; I've used it successfully...